Forage harvesters are well known in the art. They are commonly used for comminuting crop material, such as grass or maize, for silage purposes. With grass-like materials, it is sufficient to slit the crop material, i.e., the stems of the plants are cut to length using a cutter, e.g. a rotating knife drum. When cutting maize, the cobs may be slit to a smaller size but a substantial portion of the kernels remain intact. This reduces the nutrient value of the silaged crop as the kernels are more-or-less indigestible if not cracked.
In order to facilitate the complete digestion by the cattle of the crop material, including the maize kernels, the outer skin of the kernels has to be cracked or cut. Commonly, this is realized by a set of closely adjacent, co-operating compressor rolls with fluted surfaces, installed behind the knife drum and in front of the blower or accelerator, as shown for example in EP-A-0 177 995 and EP-A-0 680 687.
The crop flow between the rolls inevitably will blunt the fluted surfaces of the rolls, thus increasing the space between the rolls and reducing the cutting effect on the kernels. In order to alleviate the costs caused by the replacement of worn-out rolls, it has been proposed to use crop processor assemblies that allow for the exchange of the roll body or a section thereof alone, while preserving the shaft or shafts, and their bearings. Such assemblies have been disclosed by DE-A-43 21 898 and EP-A-0 664 077.
A constant problem with this type of exchangeable rolls is the reliable connection of the roll to the drive shaft. DE-A43 21 898, EP-A-0 995 352 and U.S. Pat. No. 6,131,837 propose to use conical rings for clamping the roll surface to the shaft. This type of connection is capable of withstanding the forces that occur during normal processing of the maize material. However, it is possible that lumps of harder material, such as stones or wood parts, are ingested by the machine and fed to the crop processor's rolls. The ensuing shocks are transmitted upon the conical shaft connections, which eventually will settle and turn loose.
Hence, there is a need for a firmer connection of the crop processor roll to the shaft, which connection however should not impede the possibility of removing and replacing the roll, whenever its surface has become blunt.